1. Field of the Invention
The present invention relates to new chiral phosphinopyrrolidine compounds and to the use of these compounds as a ligand for a metal complex compound utilizable as a catalyst for asymmetric synthesis. More particularly, the present invention relates to new chiral 2,4-diphosphinopyrrolidine compounds and to the use of these compounds as a ligand for a metal complex compound utilizable as a catalyst for a process for the asymmetric synthesis of optically active compounds by catalytic asymmetric hydrogenation of reducible compounds.
2. Description of the Prior Art
From the past, a number of researches have been made in the field of synthetic chemistry on asymmetric reducing reaction capable of synthesizing optically active compounds directly from optically inactive reducible compounds. In one of the researches, various bisphosphine ligands have been synthesized and an asymmetric reducing reaction of a reducible compound has been tested using various combinations of such ligands with a transition metal compound as catalyst. In such asymmetric reducing reaction, an optical yield (asymmetric yield) of the product and a reaction efficiency in the reaction are taken up as important factors to evaluate whether the ligand is advantageously utilizable for such reaction or not. The optical yield is the simplest way for knowing whether the ligand is effective for preparing optically active products or not. With respect to the reaction rate, a larger amount of the ligand becomes necessary in case the reaction rate is low. As a means for knowing such relation between the amount of the ligand and the reaction rate, the reaction efficiency is defined by a ratio of the substrate to the ligand in terms of molar ratio. In such asymmetric reducing reactions, however, there is not as yet found such a ligand as satisfies both of the optical yield and the reaction efficiency at the same time (B. Bosnich, "Asymmetric Catalysis" published by Martinus Nijhoff Publishers, Boston, 1986, pp. 19-31).
Under such circumstances, there is a great demand in the field of asymmetric reducing reactions for developing a new ligand which satisfies not only the optical yield but also the reaction efficiency when used as a catalyst with a metal complex for asymmetric reducing reaction of reducible compounds.